Technical Abstract:
Between d 10 and 12 of gestation, the pig embryo undergoes elongation and produces estrogen, which serves as the key molecule for maternal recognition of pregnancy. Around d 15 of gestation, the embryo begins its superficial implantation with the endometrium and a second spike in estrogen occurs from the embryo. The objective of this study was to characterize the estrogen receptors (ESR), ESR1 and 2, mRNA expression and protein localization in pig endometrium during the estrous cycle and early pregnancy. White crossbred gilts (n=30) were randomly assigned to cyclic or pregnant treatment groups. Endometrial tissues were collected, frozen and fixed at d 10, 12, 14, 16 and 18 of estrous cycle and pregnancy (n=3 per day per treatment group). Expression for ESR1 and 2 mRNA was measured using Real-time PCR and data were analyzed using GLM procedure for ANOVA. For localization of ESR1 and 2 proteins, immunohistochemistry was performed within microscopic sections of pig endometrium. Expression of ESR1 mRNA was increased (P<0.01) at d 10 of the estrous cycle and pregnancy compared with d 12, 14, 16 and 18. Interestingly, ESR1 mRNA expression was greater (P<0.05) from estrous cycle compared to pregnant, irrespective of day. In contrast, ESR2 mRNA expression was greater (P<0.05) at d 14, 16 and 18 compared to d 10 and 12 of pregnancy; however, ESR2 mRNA expression remained minimally expressed throughout the estrous cycle. Protein for ESR1 localized to nucleus of luminal and glandular epithelium and staining intensity decreased during pregnancy and the cycle. In contrast, ESR2 protein was only faintly localized to the nuclei of luminal and glandular epithelium at d 16 and 18 of pregnancy. These results suggest that ESR2 may play a role in mediating the response of the endometrium to embryonic estrogen, particularly during implantation.
USDA is an equal opportunity provider and employer.